A large quantity of exhaust gas may be produced during industrial processes such as drying and/or pyrolysis processes. The exhaust gas contains not only non-condensable process gases such as air or the like, but also a large amount of moistures including inorganic moistures such as water vapor, or organic moistures such as hexane, methanol, ethanol, and/or acetic acid, and a small amount of solid dust. It is a conventional technique to dehumidify the moisture-containing exhaust gas with a separating tower, such as a washing and cooling tower, to remove the moisture from said exhaust gas, which has been applied widely in process industries, such chemical industry (e.g., petrochemical industry, coal chemical industry, etc.), steel industry, metallurgy industries or the like.
FIG. 1 shows a conventional washing and cooling tower 90, which comprises from top to bottom: a gas outlet 901, a gas demister 902, a liquid dispenser 903, a filling unit 904 filled with one or more layers of fillers, a gas inlet dispenser 905, a liquid overflow discharge device 906 and a liquid storage region 907 at a lower part of the tower, and a liquid outlet 908 at the bottom of the tower.
As shown in FIG. 2, a moisture-containing exhaust gas for example from the drying process enters the washing and cooling tower 90 via a gas inlet 909 adjacent to the bottom of the tower, and rises up to the filling unit 904. A circulating cooling liquid condensed from the moisture enters the tower from its top, and is evenly sprayed onto the surface of the underlying filler layer through the liquid dispenser 903. In the filler layer, heat exchange and mass exchange proceed between the exhaust gas and the cooling liquid, which contact with each other in a counter-flowing manner. During this process, the exhaust gas is cooled by the cooling liquid, so that at least a portion of moisture in the exhaust gas is condensed into liquid and becomes a portion of the cooling liquid; while the exhaust gas is washed by the cooling liquid, so that the solid dust in the exhaust gas is at least partially and preferably totally removed therefrom. After passing through the filling unit 904, the exhaust gas rises in the tower and reaches the demister 902, where the exhaust gas is demisted. The demisted exhaust gas is discharged from the washing and cooling tower 90 via the gas outlet 901 by means of an induced draft fan 912. During the above-mentioned exchanging process, the cooling liquid is heated by the exhaust gas. The cooling liquid that leaves the filler layer falls to reach the bottom of the tower. A portion of the cooling liquid is discharged from the tower 90 through the overflow discharge device 906 at the bottom of the tower or a circulating cooling liquid pump 910 at the outside of the tower, and becomes a recycled moisture liquid that consists of the moisture and the dust. The remaining cooling liquid in the tower is discharged therefrom by the circulating liquid pump 910 via the liquid outlet 908, and fed into a cooling device 920 by the pump 910 for cooling. The cooled cooling liquid is fed again into the washing and cooling tower 90 to repeat the above processes.
However, such cooling tower in the prior art suffers from the following drawbacks. The recycled moisture liquid obtained from the washing and cooling tower contains not only the liquid condensed from moisture in the exhaust gas, but also solid dust entrained in the exhaust gas. Thus, a further liquid-solid separation process is required to be performed on the recycled liquid, which is technically complex and costly. Furthermore, the dust in the moisture-containing exhaust gas may also enters the circulating cooling liquid, which may block the cooling device during the cooling process for the cooling liquid, and lower the heat exchanging efficiency. Moreover, in order to perform the washing, cooling, and recycling possess, many other apparatuses or devices are needed expect for the conventional washing and cooling tower 90, so that a large work area is required.